1. Field Of The Invention
The present invention relates to an aqueous dispersion of a block copolymer. The aqueous dispersion of the invention has good adhesiveness, especially airtight adhesiveness, to various substrates, and has good stability. In addition, the aqueous dispersion of the invention gives a coating layer of good properties in water resistance, weather resistance, gloss and resistance to solvent attack.
2. Discussion of the Background
Polyolefins such as polypropylene have good properties including processability, water resistance and oil resistance, and are inexpensive. Therefore, they are widely used for plastics for electric and electronic appliances for household use and for automobile parts. In some cases, polyolefins are made into moldings coated with paint or made into laminates with other resins. However, due to their low polarity, polyolefins have a problem that they are poorly adhesive to ordinary paint and to other resins.
To solve the problem, it has been tried that the surface of polyolefin moldings are treated with chromic acid, flame, corona discharge, plasma, solvent, etc. to increase the polarity of the surface of the moldings and to improve the adhesiveness thereof to paint and other resins. However, the treatment requires complicated working steps and requires a large amount of corrosive chemicals, and is therefore often dangerous.
Under such situation, a method of applying a primer that comprises, as the essential ingredient, a chlorinated polyolefin to the surface of polyolefin moldings has been proposed. However, the chlorinated polyolefin is usually used as a solution in an aromatic organic solvent, such as toluene and xylene, which is harmful to human. Therefore, the use of a primer comprising chlorinated polyolefin is undesirable in view of environmental safety. A method of dispersing such a chlorinated polyolefin in water has been proposed (see Japanese Patent Laid-open Nos. 256556/1989 and 218548/1992). Even in this method, however, it is still difficult to prepare the aqueous dispersion without using such an aromatic organic solvent at all. In addition, the weather resistance and water resistance of the coating layer formed by the aqueous dispersion is poor.
Furthermore, aqueous dispersion type adhesive compositions free of a chlorinated substance are desired from the viewpoint of recycling or suppression of a hydrogen chloride gas generation upon waste incineration, etc.